1. Field of the Invention
The present invention relates to an aluminum nitride sintered product, a method for producing such an aluminum nitride sintered product, and an electrostatic chuck including such an aluminum nitride sintered product.
2. Description of the Related Art
Electrostatic chucks have been used for holding wafers in semiconductor manufacturing equipment. Such electrostatic chucks include an internal electrode for applying a voltage and a dielectric layer placed on the internal electrode. When a wafer is placed on the dielectric layer and a voltage is applied to the internal electrode, an electrostatic attractive force is produced between the wafer and the dielectric layer. There are electrostatic chucks employing a monopolar system in which one internal electrode is contained and electrostatic chucks employing a bipolar system in which a pair of (that is, two) internal electrodes are contained so as to be spaced apart from each other. An electrostatic chuck employing the monopolar system is configured to produce an electrostatic attractive force by applying a voltage between the internal electrode of the electrostatic chuck and an external electrode placed outside the electrostatic chuck. An electrostatic chuck employing the bipolar system is configured to produce an electrostatic attractive force by applying a voltage to a pair of internal electrodes. As for such electrostatic chucks, there is a Johnson-Rahbeck type in which a wafer is attracted with a Johnson-Rahbeck force produced using a dielectric having a volume resistivity of about 108 to 1012Ω·cm.
Materials usable for such a Johnson-Rahbeck type electrostatic chuck are, for example, aluminum nitride sintered products disclosed in Documents 1 and 2. Specifically, Document 1 discloses an aluminum nitride sintered product containing aluminum nitride as a main component, containing 0.04 mol % or more samarium in terms of oxide, and including an aluminum nitride phase and a samarium-aluminum oxide phase. Document 2 discloses an aluminum nitride sintered product containing aluminum nitride as a main component, containing 0.03 mol % or more europium in terms of oxide, and including an aluminum nitride phase and a europium-aluminum oxide phase; and also an aluminum nitride sintered product containing samarium.    Document 1: U.S. Pat. No. 6,607,836 B    Document 2: U.S. Pat. No. 7,122,490 B